A stereo amplifier or a stereo receiver? The difference being a receiver has a preamp section while an amplifier does not. You cannot hook most players directly to an amp.
Specifications will only tell you so much, and won't tell you much about build quality or features, so I'd get out and listen to some players. $100 is a bit low. The cheapest thing I would easily recommend is the Oppo 980 at $169. It is a solid all around player. Not sure about AVI, but it will do DivX.
www.oppodigital.com